1. Field of the Invention
This invention relates generally to machine tools, and more particularly to the spindle mount and drive and toolholder for a machine tool with automatic toolchanger.
2. Description of the Prior Art
The machine tool art is extensive. Vertical milling machines constitute a large component of the machine tool art. Typically they include a horizontally positionable table to hold the workpiece, a tool (usually a cutter of some type) for treating the workpiece, a powered rotating spindle for rotating the tool and vertically drivable by hand or power to advance the tool into the workpiece. More recent machines are controlled by computer and, due to their versatility, are commonly referred to as computer numerically controlled, or CNC, machining centers. They are usually equipped with some kind of automatic tool changing feature to enable the machine to make different types, sizes and contours of cuts, some of them including means for translating the workpiece mounting table or the spindle on horizontal axes automatically for contouring.
A machining center having such features is shown and described in U.S. Pat. No. 4,443,929 issued Apr. 24, 1984 to me and Walter Breitkopf. It uses an automatic tool changing feature as disclosed in more detail in U.S. Pat. No. 3,999,769 issued Dec. 28, 1976 to me and Walter Breitkopf, and which, for some features, refers to our earlier U.S. Pat. No. 3,797,956 issued Mar. 19, 1974. In that system, and referring to the reference numerals in the earlier U.S. Pat. No. 3,999,769, toolholders 58 were removably mounted in retaining rings 48 mounted in a rotatable turret plate 44 which could be indexed to place the axis of any one of the toolholders in line with a coupling plug 36 at the bottom of the tool drive spindle 30. When the turret plate was rotated to place the desired toolholder directly under and in axial alignment with the spindle, the spindle was driven downward by the spindle mounting sleeve 24 in FIG. 2 of that patent for engagement of the coupling plug 36 on the spindle with the toolholder. Further downward drive of the spindle drove the toolholder out of the turret plate and into position to engage the cutting tool therein (not shown) with the workpiece. The spindle drive motor was energized to rotate the spindle for the cutting operation, while the sleeve 24 did not rotate. The purpose of the sleeve was to contain and rotatably support the spindle and drive the spindle up and down in the housing 22. When the machining with the cutter in that toolholder was complete, the spindle sleeve was retracted and, when the plug had been pulled up to the position shown in FIG. 2, the toolholder was released into and secured in the retaining ring 48 in the turret disk. Then the turret plate 44 could be rotatably indexed to place the next desired toolholder in position under the spindle whereupon the spindle would be driven downward to connect it to the toolholder and drive the toolholder and associated tool out of the disk to engage the tool with the workpiece. The disclosures of the above-mentioned patents are incorporated herein by reference.
In machine tools, it is generally desirable to have a high degree of rigidity so that the surface which is treated (usually by cutting) on the workpiece is well within acceptable tolerance. Cutting forces transverse to the rotational axis of the tool tend to cause a bending moment from the cutter to the spindle support. The result is a certain amount of radial deflection of the spindle caused by the cutting forces. Therefore, it is an object of this invention to improve rigidity of a spindle within dimensional constraints of a machine structure.
In many machining operations, it is desirable to be able to apply a coolant to the cutting site. This is frequently done by the use of an air or liquid coolant nozzle located in the vicinity of the cutting site in the effort to direct the coolant to the cutting site. This may require some operator attention to be sure that the coolant is being applied at the proper location as different tools are applied to different locations on the workpiece. Also, and particularly where automatic tool changing is a feature of the machine, it is desirable to be certain that chips or other debris from one cutting operation do not interfere with the mating of the spindle with the next toolholder that is to be used in the succession of operations. Therefore, it is an object of this invention to provide a means whereby, in at least one embodiment, fluids can be transmitted directly down through the spindle to the toolholder.
Some combinations of cutting tools and workpiece materials perform more effectively at higher speeds. To establish optimum structural rigidity in the machine tool, the bearing size is such that, at speeds above 9,000 rpm, the bearings tend to get hot. Yet there are some applications where speeds much higher than 9,000 rpm are desirable. It is another object of the present invention to enable a machining center to perform machining operations at a much wider range of cutter speeds than heretofore available, and enable doing so with automatic tool changing features.